This invention relates to horticulture and, more particularly, to controlling the growth of vegetation, especially where there is an absence of natural light or the amount of natural light is insufficient to produce an acceptable growth rate or other desired growth characteristic of the vegetation. Specifically, the invention is directed to a method and apparatus for supplying artificial light in circumstances where there is a dearth of natural light so that an increased amount of vegetation can be grown efficiently, vegetation having more uniform foliage can be produced, and/or other selected growth characteristics, such as flower or fruit bearing, can be precisely controlled.
Most vegetation is grown with natural light, that is, sunlight. A majority of plants grown by sunlight is raised outdoors. However, greenhouses and hothouses can employ sunlight for growing vegetation indoors, especially in geographical regions remote from the equator where temperatures, as well as the insufficiency of light, can affect plant growth. Greenhouses and hothouses afford protection from freezing temperatures and frost so that plants can be grown even if the rate of growth is slow because of the small amount of sunlight. However, the deficiency of sunlight can be remedied by using artificial light in addition to sunlight for stimulating the growth of vegetation. Furthermore, even when sunlight is adequate for producing growth during certain seasons of the year, artificial light can be employed during the nighttime for enhancing growth.
Greenhouses and hothouses are not generally cost effective in extremely cold climates since they cannot typically be well insulated and at the same time admit a sufficient quantity of sunlight. Therefore, a cost effective alternative is to provide an insulated building and use exclusively artificial light for growing plants.
Additionally, vegetation which has uniform or symmetrical foliage is more healthy and, in the case of decorative plants, more salable. However, uniform foliage is not easily produced with known artificial light systems.
Furthermore, other growth characteristics of vegetation can be controlled by artificial light. These other growth characteristics include, for example, producing blooms, causing fruit to be produced, or, alternatively, stimulating the growth of foliage instead of flowers or fruit, dependent upon the nature of the vegetation being grown. Known artificial light systems often do not provide precise control of these other growth characteristics.
The use of artificial light for growing vegetation, as well as stimulating the growth of plants, and/or controlling other growth characteristics of vegetation, has increased over the years for various reasons, for example, the demand for fresh fruits and vegetables during times of the year other than the traditional growing season, the popularity of decorative tropical plants, growing plants as a hobby, propagating exotic flowers, etc. This has produced various advances in the field of artificially illuminating vegetation.
Notable among these advances are the strides made in lamp elements which serve as the source of the artificial light used for controlling the growth of plants. Metal halide, mercury vapor, and tungsten halogen grow lamps have been developed, which provide a spectrum of intense light for controlling the growth of vegetation. These grow lamps, however, are quite expensive and cost on the order of several hundred dollars a lamp fixture. In order to provide sufficient artificial light on a large or commercial scale, many such grow lamps are needed, which translates to a substantial investment in lamp fixtures. Furthermore, the operating expenses and grow lamp replacement cost can also be significant. Heretofore, there have been significant economic disadvantages to the use of these and other types of grow lamps for controlling the growth of vegetation.
Additionally, Antkowiak, U.S. Pat. No. 4,441,145, discloses a lighting system for growing plants indoors. The lighting system disclosed in this patent comprises an elongated frame forming a track, a conveyor chain trained around a drive sprocket and an idler sprocket mounted at the respective ends of the track, an electric motor connected to the drive sprocket, a carriage or carrier assembly fixed to the chain, and a lamp support chain fixed at one end to the carrier assembly and at the other end to a grow lamp. The grow lamp reciprocates along the track in a cyclic manner over the plants, thereby simulating the natural conditions of solar lighting as experienced by plants growing outdoors.
Unfortunately, the lighting system disclosed in Antkowiak, U.S. Pat. No. 4,441,145, produces nonuniform illumination of the plants as the grow lamp moves along the track, since, for example, plants at each end of the track are subjected to intense light over a single, relatively long interval, while plants below the center of the track are intensely illuminated at two separate, relatively short intervals during cyclic movement of the lamp. Also, this lighting system accommodates only a single grow lamp having a limited light spectrum, since the disposition of an additional grow lamp having a different light spectrum for producing a selected growth characteristic of the plants would result in a collision of the lamps during cyclic movement along the track.